Method and apparatus for paging a mobile terminal in a wireless lan

ABSTRACT

An apparatus and a method for implementing a paging mechanism in a wireless LAN, for example, a wireless LAN according to the Hiperlan  2  Technical Specification, for allowing a base station, or an access point, to page a mobile terminal that is not connected with, or associated with, the access point. The present paging mechanism is implemented by transmitting a broadcast channel message that includes an indication that a paging message is included in the current data frame, a second broadcast channel message that includes the information specific to the paging message, and a third broadcast channel message that include information regarding the location of the second broadcast channel message in the data frame. In response to the broadcast channel message indicating the presence of the paging request, the mobile terminal acquires the second and third broadcast channel messages and determines whether the paging request is intended for the mobile terminal.

The present invention relates to an apparatus and a method for providingpaging capability in a wireless LAN that allows a base station, or anaccess point, to send paging message to a mobile terminal that is notcurrently associated with, or connected to, the base station.

BACKGROUND OF THE INVENTION

Recently, wireless LAN technologies, such as IEEE 802.11 or ETSIHiperlan 2, have been developed that may be used in conjunction withexisting networks, including mobile networks, i.e., 3G or 2G, to providevarious services. The wireless LAN services provide the advantages offaster data speeds, generally on the order of about ten times fasterthan those provided by a 3G network, but are much more limited in thearea of coverage and the number of users that can be connected to thebase station. It is envisioned that a mobile terminal user wouldtransition from a mobile telephony network to a wireless LAN uponentering a coverage area of the wireless LAN, and transition to themobile telephony network upon leaving the coverage area of the wirelessLAN. In order to facilitate the interconnection between the servicesprovided by the mobile networks and the wireless LANs, it is desirablethat the wireless LANs provide the same services expected from a 3Gnetwork.

One such important feature of a mobile network, such as a 3G network, isthe ability to page a mobile terminal, that is, the ability for the corenetwork to page the mobile terminal that is not currently connected tothe access network. A mobile network is essentially made up of a radioaccess network and a core network. A mobile terminal has a relationshipwith the core network through the radio access network. That is a mobileterminal needs to be connected to the radio access network in order tocommunicate with the core network. During periods when the mobileterminal is not required to be directly communicating with the corenetwork the mobile terminal may enter an IDLE mode to save radioresources and to conserve power. In such a mode, the mobile terminal isnot connected with the access network. If the core network needs tocommunicate with the mobile terminal, then the core network requeststhat the radio access network page the mobile terminal. The pagingmechanism is generally implemented within the radio interface betweenthe mobile terminal and the base station. The paging process comprisesinitiating a downlink broadcast from the network to the mobile terminalthat requests that the mobile terminal connect to the radio accessnetwork. The mobile terminal determines the presence of the downlinkbroadcast, and in response, develops a connection with radio accessnetwork to communicate with the core network. In this manner, a mobileterminal does not need to be permanently connected to the radio accessnetwork, and thus, consume resources of the access network.

However, such paging capability is not available between a mobileterminal and a base station in current wireless LANs, for example awireless LAN based on the Hiperlan 2 Technical Specification. In currentwireless LAN arrangements, the mobile terminal must be permanentlyconnected to the base station, or “access point,” in order for themobile terminal to detect a downlink message. However, having a mobileterminal permanently connected to the access point requires thatresources be provisioned for that mobile terminal. In a Hiperlan 2network, connection to the access point requires that a MAC ID addressedbe reserved for that mobile terminal. However, the number of MAC IDaddresses available for a specific access point is generally limited. Ina Hiperlan 2 network, the number of addresses is limited to less than250. Therefore, a problem may arise in the availability of networkresources if the total number of mobile terminal that desire to beconnected to a particular access point, or receive downlinks through theparticular access point, exceeds 250.

Some wireless LAN arrangements, including Hiperlan 2 may allow a mobileterminal to enter a SLEEP mode, wherein the mobile terminal goes to alow power mode without losing data. In such a mode, the mobile terminalwakes up at specific intervals negotiated with the access point to checkwhether any pending messages have been buffered for the mobile terminal.If there is a pending message, the mobile terminal leaves the SLEEP modeand enters an ACTIVE mode to receive and process the pending message.However, the SLEEP mode is not suitable for implementing a pagingmechanism between the base station and the mobile terminal because themobile terminal must still connect to the base station when checking forbuffered messages. The mobile terminal is still seen by the access pointas a connected device, even while the mobile terminal is in the SLEEPmode. Therefore, a MAC ID must be allocated and some resources must beprovisioned for that mobile terminal. This means that the total numberof mobile terminals that can be connected, or periodically receivedownlink messages remains the same.

Another potential method of implementing a paging mechanism between anaccess point and a mobile terminal might be for the mobile terminal toactually disconnect from the access point and periodically connect tothe access point in order to check with the corresponding convergencelayer to determine whether downlink messages are pending. However, thisrequires the mobile terminal to initiate the association procedure eachtime it connects with the access point, which is power consuming.Furthermore, if all mobile terminals need to be periodically associatedjust for paging polling purposes, the procedure is radio resource andMAC ID consuming, whereas only one device may be affected by the paging.

Therefore, there is a need for an apparatus and a method forimplementing a paging mechanism between an access point and a mobileterminal in a wireless LAN that does not require the mobile terminals tobe permanently connected to, or to periodically associate with, anaccess point.

BRIEF SUMMARY OF THE INVENTION

In accordance with the principles of the present invention, there isprovided an apparatus and a method for implementing a paging mechanismbetween an access point and a mobile terminal that is not associatedwith, or connected to, the access point.

According to the present invention, a paging request is transmitted byan access point using a combination of a broadcast channel that istransmitted with every radio, or data, frame and indicates the presenceof a paging request, and a second broadcast channel that includes theactual data associated with the paging request. The broadcast channelinformation, or message, and the second broadcast channel information,or message, can be received by the mobile terminal while disassociatedfrom the access point. The second broadcast channel informationincludes, for example, the source identity format, the target identityformat, the source identity, and the target identity. The secondbroadcast channel information may be in the form of a transportbroadcast control message that is transmitted as necessary. A thirdbroadcast channel, which provides information regarding the location ofthe second broadcast channel within the data frame, may be included inthe radio frame.

According to the present invention, a mobile terminal that isdisassociated from the access point is configured to check, periodicallyif desired, the broadcast channel to determine the presence of a pagingrequest. If the presence of a paging request is indicated, the mobileterminal checks the second broadcast channel to determine whether thepaging request is intended for the mobile terminal. If so, the mobileterminal goes into a wake-up mode and associates with the access pointto communicate with the core network. In another embodiment, the mobileterminal checks the third broadcast channel in response to an indicationof a paging request, to receive the second broadcast channel.

In an exemplary embodiment, the paging mechanism is implemented in awireless LAN that complies with the Hiperlan 2 Technical Specification.Specifically, the indication of a paging request is transmitted in aflag within a BCCH message, and the RBCH carries the data specific tothe paging request. The FCCH message in the data frame provides thelocation of the associated RBCH message within the data frame. Theassociated RBCH is carried in a LCH and includes various information,including the source identity extension format, the target identityformat, the source identity extension, and the target identity.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described with reference to the figures, wherein:

FIG. 1 illustrates a block schematic diagram of a communications systemthat includes a plurality of wireless LANs for practicing the pagingtechnique of the present invention:

FIG. 2 illustrates the terminal stack according to the Hiperlan 2Technical Specification;

FIG. 3 illustrates the basic MAC frame according to the Hiperlan 2Technical Specification; and

FIG. 4 illustrates the format of a RBCH message adapted for implementinga paging mechanism according to the present invention.

DETAILED DESCRIPTION

The present invention provides an apparatus and a method forimplementing a paging feature in an access network such as a wirelessLAN, and in particular, a wireless LAN according to ETSI/BRAN/HIPERLAN2specifications. The paging procedure provides a method for a mobileterminal, after a first connection, to be disconnected from the accessnetwork and still be attached to the network via an upper layer entity.The upper layer entity can then request, through a paging message, thatthe mobile terminal initiate a connection through the access network asnecessary.

FIG. 1 depicts a block schematic diagram of a communications system 10that includes at least one, and preferably, a plurality of radio accessnetworks, illustratively depicted by radio access networks 11 ₁ and 11₂. The radio access networks 11 ₁ and 11 ₂ each enable at least onemobile terminal user, and preferably a plurality of users (e.g., users12 ₁, 12 ₂, and 12 ₃) to access an external data network 14 such as theInternet or the like. In a preferred embodiment, each user 12 ₁ utilizesa lap top computer to access a corresponding one of the networks 11 ₁and 11 ₂ while each user 12 ₂ utilizes a Personal Data Assistant andeach user 12 ₃ utilizes a wireless communications appliance such aswireless telephone. Other users can utilize other types ofcommunications appliances.

Each of the radio access networks 11 ₁ and 11 ₂ includes at least one,and preferably, a plurality of access points (APs), illustrativelyillustrated by APs 18 ₁-18 ₄, via which each of the mobile terminalusers 12 ₁, 12 ₂ and 12 ₃ accesses a wireless LAN 20 within each accessnetwork. In the illustrated embodiment, each AP, such as AP 18 ₁,includes a wireless transceiver (not shown) for exchanging radiofrequency signals with a radio transceiver (not shown) within thecommunications appliance employed by each user. Each of the APs 18 ₁-18₄ in each of the radio access networks 11 ₁ and 11 ₂ employs at leastone well-known wireless data exchange protocol such as the Hiperlan 2radio interface standard.

After completing a data communications session with the wireless LAN 20within a radio access network, such as radio access network 11 ₁, amobile user, such as user 12 ₃ can choose to enter a SLEEP mode toreduce the consumption of internal (i.e., battery) resources while stillretaining a connection with its associated AP (i.e., AP 18 ₃). Despitebeing in the SLEEP mode, the mobile terminal user 12 ₃ remainsassociated with the AP 18 ₃ in the radio access network and consumes anaddress and other resources to remain known to the network.

In accordance with the present principles, a mobile terminal user, suchas user 18 ₃, upon completing a data communications session, can enteran idle mode whereby the user reduces its internal (battery) resourcesand disassociates itself from its corresponding AP, (i.e., AP 18 ₃). Inthis way, the mobile terminal user 183, upon entering an idle mode, nolonger consumes an address within the AP 18 ₃, thus precluding theability of the AP to track the user. Upon receiving traffic destined forthe mobile terminal 18 ₃ currently in an idle mode, the AP 18 ₃ must insome way initiate a reconnection.

In accordance with the present principles, there is provided a techniquefor implementing a paging capability in a radio access network, such asthe radio access networks 11 ₁ and 11 ₂, which may utilize the Hiperlan2 radio interface standard, to signal a disassociated mobile user toinitiate a connection with the network. For example, the mobile terminaluser can lack an association with the radio access network because theuser has entered the above-described idle mode. Indeed, the mobileterminal user can lack an association with the radio access networkbecause the user has never had any connection at all with the network.

The network stack in a Hiperlan 2 environment is illustrated in FIG. 2,wherein the Hiperlan 2 Technical Specifications describe the PHY andData Link Control (“DLC”) layers 200 and 202 and the core networkspecific convergence layer 204. The convergence layer 204 offers serviceto and interfaces with the higher layers. The convergence layer is anadaptation layer between the network layer and the link layer. Aconvergence layer entity within the access point may broadcast data tothe peer entity with the mobile terminal. Several convergence layers mayco-exist with the mobile terminal and the access point. The PHY layer200 provides the basic data transport functions. The DLC layer 202provides for the error control (EC) function, the medium access control(MAC) function and the radio link control (RLC) function.

Hiperlan 2 sets forth various logical channels managed by the DLC layer202. The following are broadcast channels that transport generalinformation and can be used to carry a specific paging message inaccordance with the invention:

-   -   BCCH (Broadcast Channel): this channel conveys general        information about the whole cell, which comprises the radio        space covered by an access point);    -   RBCH (Radio Broadcast Channel): this channel is used to        transport broadcast control messages generated by the RLC layer.        The RLC is a sub-layer within the DLC that transports messages        relative to the attachment of the mobile terminal with the        access point; and    -   UBCH (User Broadcast Channel): this channel is used to broadcast        data from the convergence layer, which is the entity located        above the DLC layer.

The format of a MAC frame according to Hiperlan 2 is shown in FIG. 3.Each MAC frame 300 has a duration of 2 ms and consists of a sequence ofphases. The BCCH channel is transmitted in each frame 300 during theBC-phase 302. The RBCH is transmitted only when necessary duringDL-phase 304. The SLEEP mode is implemented using the BCCH. A mobileterminal wakes up regularly in order to check the BCCH according to aperiod negotiated with the access point. If the access point has apending message for a particular mobile terminal, a dedicated flag isset in the BCCH. The mobile terminal is required to check the FCCH(Frame control Channel) channel that contains indication about pendingdownlink data. The FCCH channel includes information regarding theremaining portions of the MAC frame and is transmitted during BC-phase302.

Although the BCCH may be used to trigger a wake up procedure in themobile terminal, it is not desirable to use the BCCH in implementing apaging mechanism. The size of the BCCH packet is fixed and very limitedin size. Further, the use of the BCCH to implement a paging mechanismmay preclude its use in the SLEEP mode and prevent backwardcompatibility.

In accordance with the principles of the present invention, a pagingindication is carried within a RBCH associated with the BCCH message.The RBCH is a logical channel that is mapped by the DLC over a transportchannel. Two transport channels, namely the Long Channel (LCH) and ShortChannel (SCH) may be used to carry the RBCH. The LCH is 54 bytes longand the SCH is 9 bytes. In the present invention, the LCH is utilized tocarry the paging message due to the larger size. The paging message maybe implemented using the SCH, but due to the limited size, the pagingmessage may need to be reduced or transmitted over several messagecycles. The format of a LCH for implementing the paging mechanism isillustrated in FIG. 4.

LCH paging indication 400 carries the following information. Targetidentity field 420 includes the identification of the mobile terminalbeing paged. Since the paging mechanism is used when the mobile terminalis not connected to the access point, the identity of the device is anidentity managed by an upper layer (convergence layer). The identity maybe any suitable, unique identifier associated with the mobile terminal,including, but not limited to, device identification number, subscribernumber, and URL. The format of the identity is known at this level. Theinterpretation of this field depends on the source identity. Sourceidentity field 418 provides the identity of the entity that hastriggered the paging procedure.

LCH PDU type field 402, Sequence number field 404, Extension type field408, RLC LCH PDU type field 410 and CRC field 422 represent the LCHheader, the RBCH logical channel header and the RLC header.

Extension type field 408 indicates whether the RLC message is part ofthe basic RLC protocol or part of some extensions already defined forthe home and the business environments. This proposal may beincorporated within the basic RLC as well as any extension. A potentialnew extension could be public network since one application that willuse the paging mechanism is Hiperlan 2 as an access network for a mobilenetwork. RLC LCH PDU type field 410 includes an available numberreserved for the RLC ACF (Association Control Function). The list ofnumbers is available in the Hiperlan 2 Technical Specification.

The source identity format field 416 and target identity format field417 include information that depends on the convergence layer (sourceidentity CL ID field 414). These fields may indicate a number of bytes(from 0 to 48) or a way the corresponding address is formatted. Thesource identity field 418 and the target identity field 420 are codedaccording to the format specified in the source identity format field416 and the target identity format field 417.

The steps for implementing the paging procedure is now described. Themobile terminal may be paged even though it has never been associatedwith the corresponding access point. The mobile terminal wakes upperiodically and checks the BCCH to detect whether RBCH information ispresent. If a paging request is to be broadcasted, the access pointgenerates the paging request and consecutively repeats the requestaccording to a proprietary period. If an association is performedbetween the mobile terminal and the access point the following applies.During the association procedure, the mobile terminal may exchange withthe access point various information about the capabilities of themobile terminal. The association phase may also be used to negotiate apaging group between the mobile terminal and the access point. Thepaging group corresponds to a sleeping group defined in the Hiperlan 2Technical Specification. The use of a sleeping group allows the mobileterminal and the access point to define the cycles between which themobile terminal checks the BCCH, in other words the periodicity forchecking the BCCH by the mobile terminal. Once the sleeping group isdefined, the mobile terminal is then only required to check the BCCHmessage at predetermined intervals rather than checking every BBCHmessage, thereby reducing power consumption in the mobile terminal. Thepaging mechanism according to the terminal may optionally utilize thepaging group technique to advantageously reduce power consumption by themobile terminal. Upon completion of the association procedure, themobile terminal may be disconnected, either explicitly or implicitly,from the access point and begin checking the BCCH messages according tothe negotiated paging period.

When a request to page the mobile terminal is received by theconvergence layer, the convergence layer delivers a set of requiredinformation to the DLC using a page request. In this regard, the accesspoint generates and transmits a BCCH message with a flag indicating thepresence of the RBCH having the appropriate paging information. Theaccess point also generates and transmits in the data frame a RBCHmessage having the necessary paging information. The necessaryinformation includes: paging cause, source identity CL ID, sourceidentity format, target identity format, source identity, and the targetidentity. The access point then transmits the paging indication,according to the paging groups if set, until the mobile terminalattempts to connect to the access point. The number of cycles attemptedbefore stopping the paging procedure is a configuration parameter of theaccess point.

In response to the flag in the BCCH, the mobile terminal checks the FCCHmessage to determine the transport channel location (time slot) of theRBCH. The mobile terminal then acquires and decodes the RLC LCH PDU typefield 410 to determine whether a paging indication is present. If apaging indication is present, the mobile terminal then checks theremaining fields as follows: the source identity CL ID field 414 ischecked to determine whether the paging indication came from aconvergence layer supported by the mobile terminal, if so, targetidentity 420 is checked to determine whether the paging message isintended for that mobile terminal, if so, the source identity field 418is checked to determine the paging source, and then the mobile terminalinitiates an association procedure to establish, or reestablish aconnection with the access point.

After the mobile terminal associates with the access point in responseto the paging indication, the convergence layer in the access pointsends a paging stop message to the DLC layer requesting the DLC to stopbroadcasting the associated paging request message. If there is noresponse from a mobile terminal after a predetermined period of time,the DLC may send a paging response message to the convergence layerindicating the failure of the paging attempt.

In the case of a handover, the mobile terminal changes the attachmentpoint from one access point to another. In that case, the mobileterminal may initiate an association procedure with the new access pointin order to renegotiate the paging period. Thereafter, the pagingmechanism may be utilized between the mobile terminal and the new accesspoint.

The foregoing describes an apparatus and a method for implementing apaging technique for a mobile terminal that is not currently associatedwith, or connected to, an access point in a wireless LAN. Since themobile terminal is not required to be permanently connected to theaccess point, the mobile terminal does not consume access pointresources, such as the MAC ID, and thus, potentially allows a largernumber of devices to be connected to the access point than otherwisewould be possible.

Numerous modifications to and alternative embodiments of the presentinvention will be apparent to those skilled in the art in view of theforegoing description. Accordingly, this description is to be construedas illustrative only and is for the purpose of teaching those skilled inthe art the best mode of carrying out the invention. Details of thestructure may be varied substantially without departing from the spiritof the invention and the exclusive use of all modifications, which comewithin the scope of the appended claims, is reserved.

1. A method for paging a mobile terminal that is disassociated from anaccess point in a wireless LAN, comprising the steps of: receiving apaging request from a convergence layer; generating in a link controllayer a broadcast channel message including data indicative of thepresence of the paging request; generating in the link control layer asecond broadcast channel message having data representative of thepaging request; and transmitting the broadcast channel message and thesecond broadcast channel message within a data frame.
 2. The methodaccording to claim 1, further comprising the step of: generating in thelink control layer a third broadcast channel message having dataassociated with the structure of the data frame and informationregarding the second broadcast channel message, wherein the transmittingstep comprises transmitting the broadcast channel message, the secondbroadcast channel message, and the third broadcast channel message inthe data frame.
 3. The method according to claim 2, wherein the thirdbroadcast channel message includes data indicative of the position ofthe second broadcast channel in the data frame.
 4. The method accordingto claim 2, wherein the wireless LAN comprises a wireless LAN thatcomplies with the Hiperlan 2 Technical Specification, the broadcastchannel message corresponds to a BCCH message, the second broadcastchannel corresponds to a RBCH message, and the third broadcast channelcorresponds to a FCCH message.
 5. The method according to claim 4,wherein the RBCH is carried in a LCH.
 6. The method according to claim5, wherein the RBCH includes a target identity format field, a targetidentity field, a source identity extension format field, and a sourceidentity extension field.
 7. The method according to claim 1, furthercomprising the steps of: negotiating, with the mobile terminal, aperiodic interval for checking the broadcast channel message; andtransmitting the broadcast channel message and the second broadcastchannel message only during the intervals that correspond with thenegotiated periodic intervals.
 8. The method according to claim 7,wherein the negotiated periodic interval is associated with a selectedone of a plurality of paging groups.
 9. The method according to claim 8,wherein the second broadcast channel message includes a target identityformat field, a source identity extension format field, and a sourceidentity extension field.
 10. A network access point for transmitting apaging request to a mobile terminal that is not currently associatedwith the network access point, comprising: receiving means coupled to acore network for receiving a paging request; a link control layer forgenerating a first broadcast channel message having data indicative ofthe presence of the paging request, the link control layer alsogenerating a second broadcast channel message having data representativeof the paging request; transmitting means coupled to the link controllayer for transmitting the first broadcast channel message and thesecond broadcast channel message in a data frame.
 11. The network accesspoint according to claim 10, wherein the link control layer generates athird broadcast channel message having data indicative of the locationof the second broadcast channel message within the data frame, and thetransmitting means transmits the broadcast channel, the second broadcastchannel and the third broadcast channel in the data frame.
 12. Thenetwork access point according to claim 11, wherein the transmittingmeans transmits the data frame in accordance with Hiperlan 2, thebroadcast channel message corresponds to a BCCH message, the secondbroadcast channel message corresponds to a RBCH message, and the thirdbroadcast channel message corresponds to a FCCH message.
 13. The networkaccess point according to claim 12, wherein the transmitting meanstransmits the RBCH in a LCH.
 14. The network access point according toclaim 10, wherein the transmitting means transmits the paging requestduring predetermined intervals defined by a paging group of a targetdevice.
 15. A method for controlling a mobile terminal device that iscurrently disassociated with an access point in a wireless LAN,comprising the steps of: checking a broadcast channel messagetransmitted by the access point for data indicative of a secondbroadcast channel message in the data frame; detecting, in response todata indicative of the second broadcast channel message, the secondbroadcast channel message and determining whether the message includes apaging request; determining whether the paging request is intended forthe mobile terminal device; and initiating an association procedure toestablish a connection with the access point and transmitting a responseto the paging request, in response to the determination that the pagingrequest is intended for the mobile terminal device.
 16. The methodaccording to claim 15, further comprising the steps of: detecting athird broadcast channel message having data indicative of the locationof the second broadcast channel message in the data frame, and acquiringthe second broadcast channel message in response to the third broadcastchannel message.
 17. The method according to claim 16, wherein themobile terminal operates in accordance with Hiperlan 2 TechnicalSpecification, and the checking step comprises checking a BCCH message,and the detecting steps comprise detecting a RBCH message and a FCCHmessage.
 18. The method according to claim 15, further comprising thestep of: associating with the access point to negotiate a paging group,the paging group being associated with a predetermined period intervalfor receiving paging requests, and thereafter disassociating from theaccess point and checking the broadcast channel message only during thetime intervals associated with the paging group.